Injection cartridges of the dual-chamber type are well-known and have found a wide use. They are used together with various types of injection apparatuses which serve to hold the cartridge as it is readied for injection and as injections are subsequently administered.
Injection cartridges of the dual-chamber type generally comprise a cylindrical barrel, which is shaped like a bottleneck at its front end and has an open rear end. The front end is closed by a septum of rubber or other suitable material, which is secured in place by means of a capsule. This capsule has a central opening where the septum is exposed and may be pierced by a hollow needle to establish a connection with the interior of the cartridge.
The rear end of the cartridge barrel is closed by a piston, which may be moved forward.
The cartridge is divided into two chambers by a transversal movable wall, which seals against the interior wall of the cartridge. The front chamber usually contains a solid component of the injectable preparation, while the rear chamber contains a liquid component, which is to dissolve or disperse the solid component. Through a bypass conduit arranged in the wall of the cartridge, the liquid in the rear chamber may be made to flow over into the front chamber when the movable wall is in a predetermined position.
The design and function of dual-chamber injection cartridges is well-known to those skilled in the art, and need not be described here in closer detail. In the manufacture of dual-chamber injection cartridges, the movable wall is first placed in a predetermined position in a cartridge barrel, which has been cleaned and silicone treated. The cartridges are then placed with their front ends upward, and a solution of the solid component of the injectable preparation is filled into the front chamber. The cartridges are then placed in a freeze-drying apparatus, and the solvent, which is usually water, is evaporated. After this, the cartridges are taken out from the freeze-drying apparatus, and their front openings are sealed by means of the septum and the capsule. When the front openings of the cartridges have been sealed, the rear chambers of the cartridges are filled with the liquid component of the injectable preparation, and the rear openings are sealed by means of the rear piston. This process has a number of drawbacks. The active agents are often sensitive to oxidation, which may occur when the cartridges are taken out from the freeze-drying apparatus to be sealed. Such an oxidation may lead to a degradation of the active agent of the injectable preparation. This is of special importance when the active agent is very expensive, such as growth hormones.